The transcription factor Runx1 plays a pivotal role in hematopoietic stem cell (HSC) emergence, and studies into its transcriptional regulation should give insight into the critical steps of HSC specification. Recently, we identified the Runx1 ؉23 enhancer that targets reporter gene expression to the first emerging HSCs of the mouse embryo when linked to the heterologous hsp68 promoter. Endogenous Runx1 is transcribed from 2 alternative promoters, P1 and P2. Here, we examined the in vivo cis-regulatory potential of these alternative promoters and asked whether they act with and contribute to the spatiotemporal specific expression of the Runx1 ؉23 enhancer. Our results firmly establish that, in contrast to zebrafish runx1, mouse Runx1 promoter sequences do not confer any hematopoietic specificity in transgenic embryos. Yet, both mouse promoters act with the ؉23 enhancer to drive reporter gene expression to sites of HSC emergence and colonization, in a ؉23-specific pattern. (Blood. 2009;113:5121-5124) IntroductionThe transcription factor RUNX1 is a critical regulator of definitive hematopoiesis, and genomic aberrations of the gene encoding RUNX1 are frequently found in human acute leukemia. 1 In the mouse, Runx1 null mutations result in the absence of functional hematopoietic stem cells (HSCs) and definitive progenitors, leading to embryonic lethality. [2][3][4][5][6] During development, Runx1 is first expressed in the emerging hematopoietic system, including definitive HSCs. 7,8 Its highly regulated spatiotemporal expression pattern and pivotal role in HSC emergence prompted us to study its transcriptional regulation, to obtain insight into the molecular mechanisms underlying de novo HSC generation. We recently identified the Runx1 ϩ23 hematopoietic enhancer, located 23.5 kb downstream of the ATG in exon 1. 9 We showed that this ϩ23 enhancer targets reporter gene expression, from a heterologous hsp68 core promoter, to the emerging HSCs and putative HSCfated cells in the mouse embryo, and acts directly downstream of Gata2, SCL, and Ets transcription factors. Whether the ϩ23 enhancer is equally active with the endogenous Runx1 promoters has not been assessed.Runx1 is transcribed from 2 alternative promoters ( Figure 1A), a distal P1 and proximal P2, with the P1 being specific to vertebrates. [10][11][12][13] Both the P1 and P2 promoters were reported to be transcriptionally active in the emerging hematopoietic system of the mouse embryo, at the stages of yolk sac (YS), aortagonad-mesonephros (AGM), and fetal liver (FL) hematopoiesis, with P1-derived transcripts particularly prevalent among enriched FL HSCs. 11,14,15 The P2 promoter was shown to be active in HSC-fated cells 16 and to be critically required for FL hematopoiesis. 17 In vitro transfection assays suggested that neither P1 nor P2 RUNX1 promoter elements harbored tissue-specific cis-regulatory elements. 10 However, in vivo mouse promoter assays have not been reported, and it is therefore not clear to what extent cis-elements elsewhere in the locus are req...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.